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Refactor to use .defines for many memory locations.

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This commit is contained in:
Colin McMillen 2015-05-25 14:28:00 -04:00
parent 7b6cd3f583
commit a0532f0429
1 changed files with 118 additions and 104 deletions
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222
pewpew.asm
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@ -4,19 +4,53 @@
; Assumes 16-bit X & 8-bit A.
; Memory layout:
; 0000-000F: scratch space for functions.
; 0010-0011: controller state of joypad #1.
; 0012-0013: controller state of joypad #2.
; 0014-0016: 24-bit counter of vblanks.
; 0017-0019: RGB color values to use for background color, from [0-31].
; 001A-001B: 16-bit pointer to next random byte.
; [gap]
; 0020-0021: (x, y) coordinates of player.
; 0022: shot cooldown timer.
; 0030-0032: enable / x / y of shot.
;
; Sprite table buffers -- copied each frame to OAM during VBlank, using DMA.
; 0100-02FF: table 1 (4 bytes each: x/y coord, tile #, flip/priority/palette)
; 0300-031F: table 2 (2 bits each: high x-coord bit, size)
.define joy1 $10
.define joy2 $12
.define vBlankCounter $14
.define backgroundRed $17
.define backgroundGreen $18
.define backgroundBlue $19
.define randomBytePtr $1A
.define playerX $40
.define playerY $41
.define shotCooldown $42
.define shotData $50
; TODO(mcmillen): verify that we can relocate these without messing things up.
.define spriteTableStart $100
.define spriteTable1Size $200
.define spriteTable2Start $300 ; TODO(mcmillen): use this.
.define spriteTableSize $220
; Stores result to A.
; Assumes 16-bit X & 8-bit A.
; Modifies X.
; Updates $0018-$0019 to point at the next available random byte.
; Updates randomBytePtr.
.MACRO GetRandomByte
ldx $18
ldx randomBytePtr
lda $028000, X ; $028000: beginning of ROM bank 2.
inx
cpx #$8000 ; This is the size of the entire ROM bank.
bne +
ldx #0
+
stx $18
stx randomBytePtr
.ENDM
@ -26,25 +60,16 @@
.SECTION "MainCode"
; Memory layout:
; 0000-000F: scratch space for functions.
; 0010-0011: controller state of joypad #1.
; 0012-0013: controller state of joypad #2.
; 0014-0016: 24-bit counter of vblanks.
; 0018-0019: 16-bit pointer to next random byte.
; 0020-0021: (x, y) coordinates of player.
; 0022-0024: RGB color values to use for background color, from [0-31].
; 0025: shot cooldown timer.
; 0030-0032: enable / x / y of shot.
;
; Sprite table buffers -- copied each frame to OAM during VBlank, using DMA.
; 0100-02FF: table 1 (4 bytes each: x/y coord, tile #, flip/priority/palette)
; 0300-031F: table 2 (2 bits each: high x-coord bit, size)
Start:
InitializeSNES
; By default we assume 16-bit X/Y and 8-bit A.
; If any code wants to change this, it's expected to do so itself,
; and to change them back to the defaults before returning.
rep #%00010000 ; 16-bit X/Y.
sep #%00100000 ; 8-bit A/B.
; Store zeroes to the controller status registers.
; TODO(mcmillen): is this needed? I think the system will overwrite these
; automatically.
@ -96,12 +121,6 @@ LoadPaletteAndTileData:
; quite helpful with palette / sprites / DMA, especially starting at
; http://wiki.superfamicom.org/snes/show/Working+with+VRAM+-+Loading+the+Palette
; 16-bit X/Y registers. Used for DMA source address & transfer size, both of
; which want 16-bit values.
rep #%00010000
; 8-bit A/B registers. Used for DMA source bank & destination address.
sep #%00100000
; Initialize the palette memory in a loop.
; We could also do this with a DMA transfer (like we do with the tile data
; below), but it seems overkill for just a few bytes. :)
@ -225,7 +244,7 @@ InitializeSpriteTables:
; It uses the same approach we're using, in which we keep a buffer of the
; sprite tables in RAM, and DMA the sprite tables to the system's OAM
; during VBlank.
rep #%00110000 ; 16-bit A/X/Y.
rep #%00100000 ; 16-bit A.
ldx #$0000
; Fill sprite table 1. 4 bytes per sprite, laid out as follows:
@ -236,12 +255,12 @@ InitializeSpriteTables:
; p: palette #
lda #$01
-
sta $0100, X ; We keep our sprite table at $0100 and DMA it to OAM later.
sta spriteTableStart, X
inx
inx
inx
inx
cpx #$0200
cpx #spriteTable1Size
bne -
; Fill sprite table 2. 2 bits per sprite, like so:
@ -250,10 +269,10 @@ InitializeSpriteTables:
; Setting all the high bits keeps the sprites offscreen.
lda #%0101010101010101
-
sta $0100, X
sta spriteTableStart, X
inx
inx
cpx #$0220
cpx #spriteTableSize
bne -
sep #%00100000 ; 8-bit A.
@ -268,9 +287,9 @@ InitializeWorld:
; Player's initial starting location.
lda #(256 / 4)
sta $20
sta playerX
lda #((224 - 32) / 2)
sta $21
sta playerY
rts
@ -287,14 +306,10 @@ MainLoop:
JoypadDebug:
; Load joypad registers into RAM for easier inspection.
lda JOY1L
sta $10
lda JOY1H
sta $11
lda JOY2L
sta $12
lda JOY2H
sta $13
ldx JOY1L
stx joy1
ldx JOY2L
stx joy2
rts
@ -306,104 +321,104 @@ JoypadUp:
and #$08 ; Up
cmp #$08
bne JoypadDown ; Button not pressed.
lda $21
lda playerY
cmp #0
beq JoypadDown ; Value saturated.
dec $21
dec $21
dec playerY
dec playerY
JoypadDown:
lda JOY1H
and #$04
cmp #$04
bne JoypadLeft ; Button not pressed.
lda $21
lda playerY
cmp #(224 - 32)
beq JoypadLeft ; Value saturated.
inc $21
inc $21
inc playerY
inc playerY
JoypadLeft:
lda JOY1H
and #$02 ; Left
cmp #$02
bne JoypadRight ; Button not pressed.
lda $20
lda playerX
cmp #0
beq JoypadRight ; Value saturated.
dec $20
dec $20
dec playerX
dec playerX
JoypadRight:
lda JOY1H
and #$01
cmp #$01 ; Right
bne JoypadStart ; Button not pressed.
lda $20
lda playerX
cmp #(256 - 32)
beq JoypadStart ; Value saturated.
inc $20
inc $20
inc playerX
inc playerX
JoypadStart:
lda JOY1H
and #$10 ; Start
cmp #$10
bne JoypadSelect ; Button not pressed.
lda $22
lda backgroundRed
cmp #0
beq JoypadSelect ; Value saturated.
dec $22
dec backgroundRed
JoypadSelect:
lda JOY1H
and #$20 ; Select
cmp #$20
bne JoypadY ; Button not pressed.
lda $22
lda backgroundRed
cmp #31
beq JoypadY ; Value saturated.
inc $22
inc backgroundRed
JoypadY:
lda JOY1H
and #$40 ; Y
cmp #$40
bne JoypadX ; Button not pressed.
lda $23
lda backgroundGreen
cmp #0
beq JoypadX ; Value saturated.
dec $23
dec backgroundGreen
JoypadX:
lda JOY1L
and #$40 ; X
cmp #$40
bne JoypadL ; Button not pressed.
lda $23
lda backgroundGreen
cmp #31
beq JoypadL ; Value saturated.
inc $23
inc backgroundGreen
JoypadL:
lda JOY1L
and #$20 ; L
cmp #$20
bne JoypadR ; Button not pressed.
lda $24
lda backgroundBlue
cmp #0
beq JoypadR ; Value saturated.
dec $24
dec backgroundBlue
JoypadR:
lda JOY1L
and #$10 ; R
cmp #$10
bne JoypadB ; Button not pressed.
lda $24
lda backgroundBlue
cmp #31
beq JoypadB ; Value saturated.
inc $24
inc backgroundBlue
JoypadB:
lda JOY1H
@ -419,19 +434,19 @@ JoypadDone:
MaybeShoot:
; If the cooldown timer is non-zero, don't shoot.
lda $25
lda shotCooldown
cmp #0
bne +
; Enable shot; set its position to player position.
lda #1
sta $30
lda $20
sta $31
lda $21
sta $32
sta shotData
lda playerX
sta shotData + 1
lda playerY
sta shotData + 2
; Set cooldown timer.
lda #16
sta $25
sta shotCooldown
+
rts
@ -439,17 +454,17 @@ MaybeShoot:
UpdateWorld:
; Update shot cooldown.
lda $0025
lda shotCooldown
cmp #0
beq +
dea
sta $0025
sta shotCooldown
+
; Copy player coords into sprite table.
lda $0020
lda playerX
sta $0100
lda $0021
lda playerY
sta $0101
; Set the sprite.
lda #0
@ -458,37 +473,37 @@ UpdateWorld:
lda #%00110000
sta $0103
; Clear x-MSB so that the sprite is displayed.
lda $0300
lda spriteTable2Start
and #%11111110
ora #%00000010 ; ... and make it the large size. (32x32)
sta $0300
sta spriteTable2Start
; Move shot coords.
ldx $0
lda $30
lda shotData
cmp #1
bne DisableShot
lda $31
lda shotData + 1
; TODO(mcmillen): do this with an add, then check the carry bit?
.rept 6
ina
cmp #$00 ; If it wraps around, disable it.
bne +
stz $30
stz shotData
+
.endr
sta $0031 ; Store new x-coord.
sta shotData + 1 ; Store new x-coord.
; See if sprite is still enabled after move.
lda $0030
lda shotData
cmp #1
bne DisableShot
; Set up shot sprite.
lda $0031 ; x
lda shotData + 1 ; x
sta $0104
lda $0032 ; y
lda shotData + 2 ; y
sta $0105
lda #8 ; which sprite
sta $0106
@ -500,8 +515,9 @@ UpdateWorld:
jmp ShotDone
DisableShot:
; Disable it by setting x-position to zero and setting the high x-bit.
stz $104
; Disable it by setting x-position to 1 and setting the high x-bit.
lda #1
sta $104
lda $0300
ora #%00000100
sta $0300
@ -509,11 +525,11 @@ DisableShot:
ShotDone:
; Make the background scroll. Horizontal over time; vertical depending on
; player's y-coordinate.
lda $14
lda vBlankCounter
sta BG3HOFS
lda $15
lda vBlankCounter + 1
sta BG3HOFS
lda $21
lda playerY
.rept 3
lsr
.endr
@ -525,7 +541,7 @@ ShotDone:
SetBackgroundColor:
; $22 $23 $24 are (R, G, B), each ranging from [0-31].
; The background-color bytes are (R, G, B), each ranging from [0-31].
; The palette color format is 15-bit: [0bbbbbgg][gggrrrrr]
; Set the background color.
@ -533,20 +549,20 @@ SetBackgroundColor:
stz CGADDR
; Compute and the low-order byte and store it in CGDATA.
lda $23 ; Green.
lda backgroundGreen
.rept 5
asl
.endr
ora $22 ; Red.
ora backgroundRed
sta CGDATA
; Compute the high-order byte and store it in CGDATA.
lda $24 ; Blue.
lda backgroundBlue
.rept 2
asl
.endr
sta $00
lda $23 ; Green.
lda backgroundGreen
.rept 3
lsr
.endr
@ -565,25 +581,23 @@ VBlankHandler:
VBlankCounter:
; Increment a counter of how many VBlanks we've done.
; This is a 24-bit counter. At 60 vblanks/second, this will take over
; This is a 24-bit counter. At 60 vblanks/second, this will take
; 77 hours to wrap around; that's good enough for me :)
inc $14
lda $14
inc vBlankCounter
lda vBlankCounter
cmp #$00
bne VBlankCounterDone
inc $15
lda $15
inc vBlankCounter + 1
lda vBlankCounter + 1
cmp #$00
bne VBlankCounterDone
inc $16
inc vBlankCounter + 2
VBlankCounterDone:
rts
DMASpriteTables:
rep #%00010000 ; 16-bit X/Y.
sep #%00100000 ; 8-bit A.
; Store at the base OAM address.
ldx #$0000
stx OAMADDR
@ -592,10 +606,10 @@ DMASpriteTables:
lda #$04
sta DMA0DST
; Our sprites start at $0100 in bank 0 and are #$220 bytes long.
ldx #$0100
ldx #spriteTableStart
stx DMA0SRC
stz DMA0SRCBANK
ldx #$0220
ldx #spriteTableSize
stx DMA0SIZE
; Kick off the DMA transfer.
lda #%00000001